The effect of ultrasound-assisted immersion freezing on selected physicochemical properties of mushrooms

• Effect of ultrasound-assisted freezing (UAF) on selected physiochemical properties of three mushroom varieties were studied.
• UAF significantly reduced the nucleation time and total freezing time during immersion freezing of mushroom.
• Drip losses during thawing were reduced significantly.
• UAF significantly increased the hardness of frozen-thawed mushroom.
• UAF significantly lowered polyphenol oxidase and peroxidase enzyme activity in frozen-thawed mushroom.

The application of power ultrasound during immersion freezing significantly (P < 0.05) affected freezing rate of mushrooms. Ultrasound at 0.39 W cm−2 (20 kHz) reduced nucleation time by 24%, 53% and 34% in Lentinula edodes, Agaricus bisporus and Pleurotus eryngii respectively. Drip losses during the thawing process were found to be 10% less compared to control samples. Whiteness index increased when ultrasound intensity was higher than 0.27 W cm−2 (20 kHz) in L. edodes and P. eryngii whereas, ultrasound at 0.39 W cm−2 (20 kHz) showed the highest chroma value with lower yellowness and browning indices. Ultrasound at 0.39 W cm−2 (20 kHz) resulted in the highest textural hardness values in all the three mushroom varieties. Polyphenol oxidase and peroxidase enzyme activities were also significantly (P < 0.05) reduced with the increase in ultrasound power during ultrasound-assisted freezing (UAF). These results indicated that UAF can be a suitable technology for industrial freezing of mushroom.